Quoting from Xinhuanet.com, and pictures added by the Journal:

The poet, Qu Yuan, lived in the state of Chu during the Warring States period (475 B.C. to 221 B.C.). He drowned himself in the Miluo River in today’s Hunan Province in 278 B.C., on fifth day of the fifth month of the Chinese lunar calendar, hoping his death could awaken the king to revitalize the kingdom.

The date has since been remembered as the Dragon Boat Festival, or Duanwu Festival, on which local fishermen row dragon boats along the Miluo river to search for Qu Yuan and scatter glutinous rice dumplings in the water to prevent the fish from eating his body.

And,

The appeal of traditional Chinese holidays is alleged to lie in the eating: mooncakes on the Mid-Autumn Festival, sweet dumplings on Lantern Day, and glutinous rice dumplings for Duanwu, or Dragon Boat Festival.